US8260240B2 - Single path architecture and automatic gain control (SAGC) algorithm for low power SDARS receivers - Google Patents

Single path architecture and automatic gain control (SAGC) algorithm for low power SDARS receivers Download PDF

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US8260240B2
US8260240B2 US11/204,631 US20463105A US8260240B2 US 8260240 B2 US8260240 B2 US 8260240B2 US 20463105 A US20463105 A US 20463105A US 8260240 B2 US8260240 B2 US 8260240B2
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signal
modulation type
signal modulation
transitioning
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US20070041481A1 (en
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Robert Malkemes
Denis Orlando
Jie Song
Eric Zhong
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Avago Technologies International Sales Pte Ltd
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Agere Systems LLC
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Priority to EP06254272.5A priority patent/EP1755245A3/fr
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G3/00—Gain control in amplifiers or frequency changers
    • H03G3/20—Automatic control
    • H03G3/30—Automatic control in amplifiers having semiconductor devices
    • H03G3/3052—Automatic control in amplifiers having semiconductor devices in bandpass amplifiers (H.F. or I.F.) or in frequency-changers used in a (super)heterodyne receiver
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G1/00—Details of arrangements for controlling amplification
    • H03G1/0005—Circuits characterised by the type of controlling devices operated by a controlling current or voltage signal
    • H03G1/0088—Circuits characterised by the type of controlling devices operated by a controlling current or voltage signal using discontinuously variable devices, e.g. switch-operated
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04H—BROADCAST COMMUNICATION
    • H04H40/00—Arrangements specially adapted for receiving broadcast information
    • H04H40/18—Arrangements characterised by circuits or components specially adapted for receiving
    • H04H40/27—Arrangements characterised by circuits or components specially adapted for receiving specially adapted for broadcast systems covered by groups H04H20/53 - H04H20/95
    • H04H40/90—Arrangements characterised by circuits or components specially adapted for receiving specially adapted for broadcast systems covered by groups H04H20/53 - H04H20/95 specially adapted for satellite broadcast receiving
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04H—BROADCAST COMMUNICATION
    • H04H20/00—Arrangements for broadcast or for distribution combined with broadcast
    • H04H20/20—Arrangements for broadcast or distribution of identical information via plural systems
    • H04H20/22—Arrangements for broadcast of identical information via plural broadcast systems
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

Definitions

  • the present invention relates to automatic gain control in radio receivers, and particularly to automatic gain control in digital radio receivers adapted for receiving multiple types of signal using a single path of radio frequency and intermediate frequency (RF/IF) front end and a single analogue-to-digital converter.
  • RF/IF radio frequency and intermediate frequency
  • Satellite digital audio radio services broadcast audio programming directly from a satellite to an end user's radio receiver, so that a typical SDARS broadcast reaches an extensive, diverse, geographical region.
  • SDARS providers typically complement their satellite broadcast with gap-filling rebroadcasts using terrestrial stations located in regions having poor or no satellite reception, such as cities with tall buildings.
  • the signals broadcast from the satellite and by the terrestrial stations contain the same audio data, and are typically on adjacent frequencies but use different modulation techniques.
  • the terrestrial signals are also typically broadcast at significantly higher signal strength, primarily because terrestrial stations have easy access to electrical power while satellites are limited to the electrical power available from their solar panels.
  • An exemplary SDARS system is the service provided by Sirius Radio Systems of New York, N.Y., which broadcasts over 100 channels of audio programming directly from satellites to users equipped with appropriate receivers.
  • FIG. 1 shows the relative frequencies and power levels of the signals in the Sirius system.
  • Two geo-synchronous satellites transmit S band (2.3 GHz), time division multiplexed (TDM) signals directly to the end user's receiver, which is typically a mobile receiver in an automobile or a truck.
  • TDM time division multiplexed
  • terrestrial repeater stations broadcast a coded orthogonal frequency division multiplexed (COFDM) signal containing the same audio data as that broadcast in the satellite signals.
  • COFDM coded orthogonal frequency division multiplexed
  • FIG. 2 shows a schematic diagram of a prior art, digital radio receiver designed to receive and decode the audio channels contained in the Sirius system signals.
  • the receiver 10 has two decoding circuits 12 and 14 , one for receiving TDM signals directly from the satellites and one for receiving COFDM signals.
  • the TDM decoding circuit has a TDM antenna 16 for receiving the signal, which is then amplified by TDM variable gain amplifier (VGA) 18 .
  • VGA variable gain amplifier
  • the amplified signal is digitized by a TDM analogue-to-digital converter (ADC) 20 .
  • the digitized TDM signals are down-converted by TDM digital-down-converter (DDC) 22 , before being demodulated.
  • TDM demodulators 24 and 26 one for handling each of the signals.
  • the ADC 20 which is typically a 10 bit device with a usable dynamic range of about 52 dB, plays an important role in digital radio reception. As long as the digitized signal is an accurate representation of the incoming analogue signal, digital filtering techniques make it possible to extract very weak signals, such as those received from a satellite, even in the presence of a significant amount of noise. Accurate digitization requires that the incoming signal is amplified sufficiently to fill as much of the ADC's dynamic range as possible. It is, however, also very important not to over amplify the incoming signal since, when the ADC is overdriven and overflows, a small signal in a noisy background can be completely lost. This happens because the ADC simply truncates any excess signal.
  • the appropriate gain setting of VGA 18 that amplifies the incoming signal to the optimal level for the ADC is controlled by the TDM automatic gain control (AGC) 28 .
  • the AGC monitors the demodulated TDM signals, and uses the stronger of the two demodulated TDM signals to set the gain of VGA 18 so that the portion of the received signal containing the best TDM signal is amplified appropriately, and a constant level output is obtained.
  • Any available COFDM signal is demodulated using a parallel COFDM decoding circuit 14 , having COFDM antenna 30 , VGA 32 , ADC 34 , COFDM 36 , COFDM demodulator 38 , and COFDM AGC 40 . All the demodulated signals are summed together in sum module 42 .
  • the front end of both the TDM and the COFDM decoding circuits contain substantially identical components, i.e., the TDM and COFDM antennas 16 and 30 , VGAs 18 and 32 and ADCs 20 and 34 are the same as each other.
  • the TDM and COFDM antennas 16 and 30 VGAs 18 and 32 and ADCs 20 and 34 are the same as each other.
  • ADC analogue-to-digital converter
  • VGA gain settings for the two types of signal may be incompatible with each other. This causes difficulties if the VGA gain is controlled using a simple, two-state AGC 43 , with one state to optimize the gain for a COFDM signal and one state to optimize the VGA gain for a TDM signal.
  • a VGA gain that is optimal for the weak TDM signals from the satellite will typically over-amplify the incoming COFDM signal from the terrestrial stations, resulting in the COFDM signal over-flowing the ADC's dynamic range.
  • This over-flow of the ADC's dynamic range means that the demodulated COFDM audio data is of very poor quality, and may even be non-existent.
  • the receiver may also be blocked from reception of the TDM signal.
  • the VGA gain setting is optimal for the ADC to digitize the portion of the signal containing the stronger, COFDM signal
  • the portion of the signal containing the TDM signal will be under-amplified, and poorly digitized by the ADC.
  • the result is that if the receiver does lock on to a terrestrial COFDM signal, it may stay locked onto the terrestrial signal, even if there is a better satellite signal available.
  • the present invention provides automatic gain control (AGC) methods and apparatus for use in a digital radio receiver that allows at least two types of input signal to be processed using a single receiver front end, i.e., a single antenna, VGA and analogue-to-digital converter (ADC) combination, that is common to the decoding circuits used for all types of signal.
  • ADC automatic gain control
  • the AGC of this invention enables single front-end processing of two different signal types by supporting two modes of operation, each optimized for supporting one particular signal type, and a third mode of operation which is capable of supporting both modes, but is not optimized for either.
  • the AGC enables the receiver to switch between the optimized modes of operation via the non-optimized mode, thereby allowing for smooth transitions between the optimized modes of operation.
  • the AGC monitors the demodulated output of each signal type, and by comparing the signal strengths, makes transitions between the three modes of operation.
  • the AGC measures the difference between the strength of the demodulated signals of each type of signal. This difference is compared to two preset, threshold values. If, while the receiver is in the third, non-optimized mode of operation, this difference has a value that is between the two threshold values, the receiver remains in the third, non-optimized mode of operation. If, however, while the system is in this third mode of operation, the difference has a value that is less than the first, lower threshold value, the system transitions to a first mode of operation optimized for the first type of signal.
  • the system transitions back to the third mode of operation.
  • the receiver transitions to a second mode of operation optimized for the second type of signal. If, while the system is in this second mode of operation, the difference falls below the second threshold value, the receiver transitions back to the third mode of operation.
  • the AGC adjusts the gain of a VGA so that an incoming signal is amplified to a level that is suitable for an analogue-to-digital (ADC) converter to convert the required signal type to a digital form.
  • ADC analogue-to-digital
  • FIG. 1 shows the relative frequencies and power levels of the signals in an exemplary satellite digital audio radio (SDARS) system.
  • SDARS satellite digital audio radio
  • FIG. 2 is a schematic diagram of a digital radio receiver designed to receive and decode the audio channels contained in the exemplary SDARS system of FIG. 1 .
  • FIG. 3 is a schematic diagram of a digital radio receiver having a single front-end and being capable of receiving and decoding the audio channels contained in the exemplary SDARS system of FIG. 1 , but having a two-state AGC.
  • FIG. 4 is a schematic diagram of a digital radio receiver having a single front-end and being capable of receiving and decoding the audio channels contained in the exemplary SDARS system of FIG. 1 , but having a four-state AGC.
  • FIG. 5 is a state-transition diagram for a single path automatic-gain-control (AGC) suitable for controlling a single front-end digital radio receiver of the type shown in FIG. 3 .
  • AGC automatic-gain-control
  • the present invention provides an automatic gain control (AGC) that enables a digital radio having a single front-end to process multiple, different input signals.
  • AGC automatic gain control
  • the AGC does this by having a number of modes of operation, each characteristic of a specific reception environment that the receiver may be used in, and a decision making algorithm for switching among these modes of operation.
  • a digital radio receiver having a single front-end, i.e., a single antenna, a single path of VGA, and a single analogue-to-digital converter (ADC), and a plurality of back-ends, i.e., a plurality of digital down converters (DDC) and digital demodulators, is controlled by means of a single AGC.
  • the AGC is capable of setting and maintaining the gain of the VGA so that the signal at its output can be maintained at a plurality of set points. Each set point is chosen for substantially optimal decoding of the types of signal typically available to the receiver in a particular reception environment.
  • the AGC is further capable of monitoring and comparing the demodulated signals of each of the plurality of receiver back-ends, and using the comparison to decide whether to transition to another set point.
  • the AGC of the present invention avoids having the receiver either lock onto a poor signal because a better signal is under-amplified at a particular set point, or being blinded to a better signal because a poorer signal is over-flowing the ADC at a particular set point. In this way, the AGC ensures that the best available signal is used at all times.
  • the AGC of the present invention is particularly suited to use in satellite digital audio radio (SDARS) systems, particularly those in which a gap-filling terrestrial repeater broadcasts a complementary signal containing the same audio data, as it allows the use of single VGA and ADC, thereby considerably reducing the cost and power requirements of such receivers. Furthermore, the AGC system and method is compatible with existing SDARS transmission capabilities. Such a terrestrial repeater typically broadcasts on a frequency adjacent to the satellite broadcast signal, but using a different modulation method and at a significantly different signal strength.
  • SDARS satellite digital audio radio
  • a typical SDARS transmission system which includes two visible satellites and also gap-filling terrestrial repeaters in some locations, has at least four environments in which a receiver has to operate.
  • a first environment is open space, where satellite reception is good and there are no repeater stations, such as in a flat rural area.
  • this first environment only satellite broadcast signals are available and the receiver has to select only which satellite broadcast signal is the best to use.
  • a second environment is a region with poor or no satellite reception, but with good terrestrial reception.
  • An example of such an environment is New York City, where the tall buildings block satellite reception. In such a region, the radio receiver only needs to decode the terrestrially broadcast signal.
  • a third environment is a transition region in which signals from both a satellite and from a terrestrial repeater are available at acceptable signal strengths.
  • An example of such a region is the beltway around Washington, D.C.
  • the radio receiver has to choose which signal provides the best quality audio data after decoding.
  • a fourth environment is a region where the satellite broadcast signal is poor or non-existent and the terrestrial reception is poor.
  • An example of such a region is Newark, N.J., where the buildings are tall enough to make satellite reception problematic but which is not adequately served by terrestrial broadcast stations.
  • a preferred embodiment of the invention comprises an AGC having four operational modes. Each operational mode provides substantially optimal decoding of the SDARS signals available to the receiver in one of the four reception environments detailed above.
  • Each operational mode provides substantially optimal decoding of the SDARS signals available to the receiver in one of the four reception environments detailed above.
  • FIG. 4 is a schematic diagram of a digital radio receiver having a single front-end and being capable of receiving and decoding the audio channels contained in the exemplary SDARS system of FIG. 1 , and in which the VGA gain is controlled by a four-state AGC.
  • the digital radio receiver 46 comprises an antenna 16 , a VGA 18 , an analogue-to-digital converter 20 , a COFDM digital down converter (DDC) 36 , a COFDM demodulator 38 , a TDM DDC 22 , a first TDM demodulator 24 , a second TDM demodulator 26 , a signal mixer 42 and a single path Automatic Gain Control (SAGC) 44 .
  • the SAGC 44 comprises monitor inputs, including COFDM demodulator output monitor line 52 , COFDM DDC pre-filter power output line 49 , TDM 1 monitor line 50 and TDM 2 monitor line 48 .
  • the COFDM demodulator output monitor line 52 contains two signals, the post-filter power of the COFDM signal, P 0 , and the COFDM track signal that indicates whether or not any COFDM signal is currently being tracked.
  • the TDM 1 demodulator output monitor line 50 also contains two signals, the power of the TDM 1 signal, P 1 , and the TDM 1 track signal that indicates whether or not any TDM 1 signal is currently being tracked.
  • the TDM 2 demodulator output monitor line 48 contains two signals, the power of the TDM 2 signal, P 2 , and the TDM 2 track signal that indicates whether or not any TDM 2 signal is currently being tracked.
  • AGC 44 sets the gain of VGA 18 based on the monitored signals.
  • the digital radio receiver 46 is comprised of electronic circuits that are well known in the art and can be manufactured by well known electronic component techniques, or implemented entirely, or in part, on general purpose computing and control devices such as, but not limited to, digital signal processors.
  • FIG. 5 is a state-transition diagram for a single path automatic-gain-control (AGC) suitable for controlling the single front-end digital radio receiver of FIG. 3 .
  • the state transition diagram comprises four distinct states of operation, States 1 - 4 . These four states correspond to the reception conditions detailed above.
  • the AGC 44 sets the gain of VGA 18 to substantially optimize processing of the signal expected in the first reception environment, so as to yield the most accurate data after decoding.
  • the VGA gain is set to substantially optimally amplify a TDM signal received from a satellite.
  • the AGC 44 sets the gain of VGA 18 to substantially optimize processing of the signal expected in the second reception environment, so as to yield the most accurate data after decoding.
  • the VGA gain is set to substantially optimally amplify a COFDM signal received from a terrestrial broadcast station.
  • the AGC 44 sets the gain of VGA 18 to process both types reasonably, so as to yield acceptable data from both signals after decoding.
  • the AGC sets the gain of VGA 18 to an intermediate or compromise value that substantially ensures that both a TDM signal received from a satellite and a COFDM signal received from a terrestrial broadcast station will yield usable audio data after decoding.
  • the AGC 44 sets the VGA gain to optimize the demodulation of the COFDM signal in order to operate in the environment in which there is no satellite broadcast signal and the terrestrial signal is weak.
  • the VGA gain in State 4 is the same as State 2 , it is shown as a separate state because the conditions for transitioning into and out of State 4 are different from those for transitioning into and out of State 2 , as described in detail below.
  • the transitions between the four states are managed according to the transition rules diagramed in FIG. 4 .
  • AGC 44 calculates a difference between the power level P 0 of the demodulated, terrestrial COFDM signal, and the greater of power levels P 1 and P 2 .
  • P 1 and P 2 are the power levels of the demodulated, satellite broadcast TDM signals). This difference is then compared with two preset threshold values, a lower value D 1 and an upper value D 2 . Depending on this comparison, and on which state the receiver is currently operating, various transitions are made.
  • receiver 46 if receiver 46 is operating in the State 3 mode in which the AGC is set to a compromise value to allow reasonable decoding of both types of signal, and the difference is less than the upper value D 2 , and greater than, or equal to, the lower threshold value D 1 , the receiver 46 continues to operate in the State 3 mode, as indicated by transition 54 . If the receiver is in the State 3 mode and the difference falls below lower threshold D 1 , AGC 44 transitions receiver 46 along transition 56 to operate in the State 1 mode, optimized for demodulating data contained in a satellite broadcast TDM signal.
  • transitions from the State 3 mode of operation include: the transition 58 , in which the difference is greater than, or equal to, the upper threshold value and therefore transitions to State 2 , in which the AGC 44 optimizes for a COFDM signal; and transition 60 , in which the AGC 44 detects no TDM track signal and therefore transitions to State 4 , in which the AGC 44 optimizes for a COFDM signal.
  • the transitions from the State 1 mode of operation, in which the AGC optimizes for a TDM signal include: the transition 62 , of remaining in State 1 mode if the difference is less than lower threshold D 1 ; the transition 64 to the State 3 mode of operation, in which the AGC 44 uses a compromise setting to allow reasonable decoding of both a TDM and a COFDM signals, if the difference is greater than or equal to the lower threshold D 1 ; and the transition 66 to the State 4 mode of operation, in which the AGC 44 optimizes for a COFDM signal, if no TDM track signal is detected.
  • the transitions from the State 2 mode of operation, in which the AGC 44 optimizes for a COFDM signal include: the transition 68 of remaining in the State 2 mode of operation if the difference is greater than or equal to the upper threshold value; and the transition 70 to the State 3 mode of operation, in which the AGC is set to a compromise value to allow reasonable decoding of both types of signal, if the difference falls below the upper threshold value D 2 .
  • the transitions from the State 4 mode of operation, in which the AGC 44 optimizes for a COFDM signal include: the transition 72 of remaining in State 4 if the difference is less than the upper threshold value D 2 ; the transition 74 to the State 2 mode of operation in which the AGC 44 uses a compromise setting to allow reasonable decoding of both a TDM and a COFDM signals, in which the AGC 44 optimizes for a COFDM signal, if the difference is greater than, or equal to, the upper threshold D 2 ; and the transition 76 to State 3 mode of operation, in which the AGC if no COFDM track signal is detected.
  • a hysteresis off-set value i.e. a value that is different depending on the history of the system.
  • the hysteresis off-set value is used to prevent repetitive switching when the difference value is close to the preset value.
  • the transitions between the states in one direction only occur if the difference exceeds the preset values by the amount of the hysterisis off-set value, while transitions between the same states in the opposite direction only occur if the difference is less than the preset values by the amount of the hysteresis off-set value.
  • transition 58 from State 3 to State 2 only occurs if the difference value is greater than or equal to the preset value plus the hysteresis off-set value
  • transition 70 from State 2 to State 3 only occurs if the difference is less than the preset value minus the hysteresis off-set value. This prevents repetitive switching between states 2 and 3 when the difference value is close to a preset value.
  • an assurance time which is a preset time value.
  • transitions between the states as detailed above, only occur if a transition condition is maintained for a length of time that is at least equal to the preset time value.
  • the states and the transitions between them may be implemented by programming a general purpose digital computing and control device such as, but not limited to, a digital signal processor or a digital micro-processor.
  • Appendix I is a listing of computer code for implementing an exemplary embodiment of the invention on such a device, including typical, practical gain and threshold values.
  • the AGC may monitor other attributes of the demodulated signals including, but not limited to, the signal-to-noise ratio of the signal. Comparisons of these attributes may be used in a manner similar to the way in which power levels are used in the embodiments of the invention detailed above. For instance, a difference in the signal-to-noise ratio of the decoded satellite signal and the signal-to-noise ratio of the decoded terrestrial signal may be use to adjust the gain of the VGA according to the inventive concepts of the present invention.

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  • Physics & Mathematics (AREA)
  • Astronomy & Astrophysics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Circuits Of Receivers In General (AREA)
  • Control Of Amplification And Gain Control (AREA)
  • Time-Division Multiplex Systems (AREA)
US11/204,631 2005-08-16 2005-08-16 Single path architecture and automatic gain control (SAGC) algorithm for low power SDARS receivers Active 2028-12-23 US8260240B2 (en)

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US11/204,631 US8260240B2 (en) 2005-08-16 2005-08-16 Single path architecture and automatic gain control (SAGC) algorithm for low power SDARS receivers
EP06254272.5A EP1755245A3 (fr) 2005-08-16 2006-08-15 Architecture à voie unique et algorithme de contrôle de gain automatique pour des récepteurs SDARS à faible consommation
JP2006221864A JP5078301B2 (ja) 2005-08-16 2006-08-16 低電力ｓｄａｒｓ受信機用の単一経路アーキテクチャおよび自動利得制御（ａｇｃ）アルゴリズム

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US7809343B2 (en) 2007-04-25 2010-10-05 Agere Systems Inc. Multi-channel receiver with improved AGC
US7769357B2 (en) * 2007-04-25 2010-08-03 Agere Systems Inc. Multi-channel receiver with improved AGC
CN101075832B (zh) * 2007-06-26 2011-07-13 京信通信系统（中国）有限公司 一种应用于tdma系统中的全数字agc控制方法及其系统
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US9338668B2 (en) * 2012-11-07 2016-05-10 Qualcomm Incorporated Gain control for intra-band carrier aggregation
US9591595B2 (en) * 2014-09-30 2017-03-07 Hughes Network Systems, Llc Inroute automatic gain control detection of outroute interference
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JP2007053766A (ja) 2007-03-01
JP5078301B2 (ja) 2012-11-21
EP1755245A3 (fr) 2014-08-20
US20070041481A1 (en) 2007-02-22

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